With a rapid growth of video services and cloud services, operators pay special attention to flexibility of optical network construction, and reduction of costs of construction, operation, and maintenance of an optical network. There are increasingly more direction dimensions (or, transmission paths) on which a network node needs to be cross-connected. Instead of performing previous manual exchange of an optical fiber connection, an operator can remotely and automatically perform dimension switching or the like by using a reconfigurable optical add/drop multiplexer (ROADM), thereby satisfying a dynamic network connection need.
Currently, it is known that, an ROADM has N input ports that are one-dimensionally arranged, M output ports that are one-dimensionally arranged, and two levels of optical switch arrays; and can split a wavelength division multiplexing (WDM) signal, which is from each input port, into K sub-signals by using a grating, switch each sub-signal to a corresponding optical switch unit in a second-level optical switch array (which has M×K optical switch units that are two-dimensionally arranged) by using a first-level optical switch array (which has N×K optical switch units that are two-dimensionally arranged), can combine sub-signals into a WDM signal by using the grating, where the sub-signals are from the second-level optical switch array, have different wavelengths, and correspond to a same output port, and can transmit the WDM signal to the corresponding output port, so as to complete network cross connect.
To adapt to needs of a high-speed optical communications network for high efficiency and flexibility, the ROADM, which is used as a core of network cross connect, needs to develop constantly, and it is intended that the ROADM can have more output ports, to implement crossing of signals of more output dimensions. As described above, in a case in which a crossing capability (for example, a rotation range) of a single optical switch is enough, a quantity K of sub-signals included in the WDM signal (specifically, a quantity of wavelengths of the included sub-signals) is relatively large and is relatively fixed, and therefore, a crossing capability that is of the ROADM and that is for an input end mainly depends on a quantity, that is M, of optical switch units that are in the second-level optical switch array and that correspond to the output ports. Limited by configuration space, the crossing capability of the single optical switch unit, and the like, M cannot increase infinitely, which cannot satisfy currently increasing quantities of network needs and user requirements.
Therefore, it is intended to provide a technology that can improve, within given limited configuration space, a network cross connect capability that is of the ROADM and that is for an output end.